High surface area porous silicon (PS) substrates formed in wafer scale through electrochemical (EC) etching fall into two groups. PS substrates fabricated from aqueous electrolytes consist of highly branched nonporous substrates while PS substrates fabricated from an aqueous electrolyte are comprised of open and accessible macroporous substrates with deep, wide, well-ordered channels.
High-surface area silicon substrates formed in wafer scale through etching display a visible photoluminescence (PL) upon excitation with a variety of visible and ultraviolet light sources. This room-temperature luminescence has attracted considerable attention primarily because of its potential use in the development of silicon-based optoelectronics, displays, and sensors.
Although the PL is thought to emanate from regions near the PS substrate surface, the origin of the PL is the source of some controversy as the efficiency and wavelength range of the emitted light can be affected by the physical and electronic properties of the surface, the nature of the etching solution, and the nature of the environment into which the etched sample is placed. Given this range of parameters, it is surprising that, with few exceptions, PL spectra are reported for PS substrates formed in dilute aqueous HF solutions, that have already been dried in air or more inert environments following etch and rinse treatments. These ex situ samples, while providing spectral information, do not indicate the evolution of the PS substrates, and thus, they do not indicate means by which it might be modified and enhanced during or following the etch treatment.
An existing problem in fabricating PS devices rests with establishing electrical contact to the PS substrates. Another problem with PS includes the relatively long excited-state lifetime associated with the PS substrate PL. A further problem includes the relatively low PL quantum yield and the instability of the PL from PS substrates. An additional problem includes that small, sensitive, and selective sensors are not readily available at cost effective prices.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.